Process for preparing yarn packages

ABSTRACT

PROCESS AND APPARATUS FOR MINIMISING THE VARIATION IN THROUGHT PACKAGE RETRACTION THAT OCCURS IN PACKAGES OF FRESHLY DRAWN THERMOPLASTIC YARN BY HEATING THE YARN AFTER DRAWING ACCORDING TO A DEFINED PROGAMME.

Nov. 13, 1973 I G. THOMAS ETAL 3,772,415

PROCESS FOR PREPARING YARN PACKAGES Filed Dec. 13, 1971 FIGQI FINTEMPERATURE PACKAGE WEIGHT (o2) FIG.2

O/OYARN RETRACTION OVER 24 HOURS United States Patent 3,772,415 PROCESSFOR PREPARING YARN PACKAGES Gwylfa Thomas and Brian William Jenkins,Pontypopl, England, assignors to Imperial Chemical Industries Limited,London, England Filed Dec. 13,1971, Ser. No. 207,247 Claims priority,application Great Britain, Dec. 16, 1970, 59,716/70 Int. Cl. B29c 25/00U.S. Cl. 264-234 4 Claims ABSTRACT OF THE DISCLOSURE Process andapparatus for minimising the variation in through package retractionthat occurs in packages of freshly drawn thermoplastic yarn by heatingthe yarn after drawing according to a defined programme.

The present invention relates to retraction uniformity in yarn packagesand particularly though not exclusively to a process and apparatus forachieving such uniformity.

conventionally, and in order that (monoor multifilament) yarns derivedfrom synthetic thermoplastic polymers such as polyamides and polyestersmay be usefully employed in normal textile operations, they must bemolecularly orientated or stretched (drawn) after extrusion andsolidification from the molten polymer. The drawing process may beconveniently carried out by passing the yarn sequentially around tworolls which are rotated at different speeds, thus, if the second roll(draw roll) is rotated, say, at three times the speed of the first (feedroll), the yarn will be stretched by that amount between them. Finally,the drawn yarn, usually under some degree of relaxation, is wound eitherdirectly or indirectly on to a bobbin by, say, a ring and travellerassembly which simultaneously inserts a small amount of stabilisingtwist into the yarn.

Freshly drawn yarn, however, though wound on to a I bobbin is stilltending to shrink and in these circumstances a situation somewhat akinto the following arises. The innermost package layers because they areheld firmly against the container barrel are unable to shrink, while theouter package layers shrink to some extent onto the layers beneath. Themiddle package layers are less free to shrink and are subjected tocrushing due to the shrinkage of the outer layers. Thus, when yarn istaken from the package, the residual tendency to shrink or retract islowest in yarn from the middle of the package and greatest in yarn fromthe inside.

In practice this variation in retraction manifests itself as anundesirable variation of dye up-take (stripiness) in a final woven orknitted fabric, and arises not only from a variation of retractionthrough a single yarn package, but from the jump in retraction thatoccurs when yarn from one package is joined to yarn from another, as inmagazine creeling, since it is yarn from the inside of one package thatis joined to yarn from the outside of another.

In the present invention the applicants have sought to minimise thisvariation in retraction in freshly drawn yarn packages by heating thefreshly drawn yarn in a defined manner before Winding up.

Thus, the present invention provides a process for minimising thevariation in through package retraction that occurs in packages offreshly drawn thermoplastic yarn in which the yarn after drawing andprior to being wound onto a bobbin is heated to gradually decreasingtemperatures until a minimum temperature is reached and thereafter isheated to gradually increasing temperatures, the changes in temperaturecorresponding to the substantial changes in retraction that wouldotherwise occur through the package.

3,772,415 Patented Nov. 13, 1973 The present invention also provides athermoplastic yarn drawing apparatus for carrying out the above proc essin which variable heating means are located between the draw roll andyarn wind up means.

Roughly speaking, the gradual decreasing and increasing yarn temperatureoccurs, respectively, during the winding of the first and final thirdsof the yarn package.

Besides minimising variation in through package retraction, the processand apparatus of the present invention also reduce the overall level ofretraction that occurs in freshly drawn yarn. Thus, although directed tothe reduction of variation in through package retraction, the practiceof the present invention results in an overall reduction in themagnitude of any residual retractive forces that might arise in packagesof freshly drawn yarn.

One convenient way of heating the freshly drawn yarn according to thepresent invention is to locate the heating means in the form of anelectrically heated pin or plate immediately after the draw roll in thedrawing process, though the heating device may be located furtherdownstream of the draw roll should such an arrangement prove attractivein terms of apparatus geometry.

The applicants prefer to use a 4 inch diameter heated matt chrome pinlocated immediately after the draw roll.

In the following example of the present invention which is by way ofillustration only, a 40 denier 13 filament yarn derived frompolyhexamethylene adipa'mide was drawn at 2,646 f.p.m. and passed arounda 4 inch diameter heated matt chrome pin located immediately after thedraw roll in a conventional drawtwister machine. The yarn was wound upwith a ring and traveller assembly at constant spindle speed to form a32 oz. multicycle yarn package.

During the winding of approximately the first 10 ozs. of yarn, thetemperature of the heated pin was gradually decreased from 150 C. to 70C., and then after approximately 20 ozs. of yarn had been wound thetemperature of the pin was gradually increased to 150 C. again at 32ozs.

FIGS. 1 and 2 show respectively, according to the above example, thechange in pin temperature and the change in percentage yarn retractionwith increasing package Weight. It will be apparent that each unitlength of yarn is heated to essentially one temperature which isdifferent for each unit length.

In FIG. 2, for comparative purposes, the change in percentage yarnretraction when a heated pin was not employed is shown at A.

Yarn retraction is defined as the reduction in length which occurs inyarn suspended vertically under a stress of 0.002 to 0.007 gm./d. in airover a period of at least 24 hours. In the present invention retractionwas determined by cutting a measured length of yarn (1.5 metres) from athreadline at a tension of 0.005 to 0.05 gm./d. running at a speed of 5m./sec., and freely suspending this length under a weight correspondingto 0.002 gm./d. for the required period. Retraction is then expressed asa percentage change of the original cut length. Prior to thedetermination the yarn package to be tested was conditioned for at least24 hours in the atmosphere in which the test was conducted, i.e. in airat 18 C.-27 C. and

59 7 1 relative humidity.

When knitted fabrics comprising yarn of the above example were dyed withChlorazol violet or Solway blue BN, no stripiness due to yarn retractionvariations was visible. In similar fabrics comprising untreated yarns,stripes were clearly visible after dyeing.

What is claimed is:

1. In a process for drawing and winding polyamide yarn onto a bobbin toform a package, the improvement which minimizes the variation in throughpackage retraction that occurs in packages of freshly drawn yarn, saidimprovement comprising after drawing and prior to winding the yarnheating the yarn by heating means, decreasing the temperature of theheating means during winding to a minimum temperature and thereafterincreasing the temperature again before winding is completed, thechanges in temperature corresponding to the substantial changes inretraction that would otherwise occur through the package.

2. A process according to claim 1 in which a gradual decreasing andincreasing of the temperature of the heat ing means occurs respectivelyduring the winding of the first and final thirds of the yarn package.

3. A process according to claim 1 in which the yarn is Wound onto abobbin rotated at constant speed.

4. In a process for drawing and winding polyamide yarn onto a bobbin toform a package, the improvement which minimizes the variation in throughpackage retraction that occurs in packages of freshly drawn yarn, saidimprovement comprising after drawing and prior to winding the yarncontinuously heating the running yarn to a gradually decreasingtemperature during winding of about the first one-third of the packageand thereafter gradually increasing the temperature of the running yarnduring winding of about the final one-third of the package.

References Cited UNITED STATES PATENTS 2,794,700 6/ 1957 Cheney 264-3462,952,033 9/1960 Goodwin 264346 3,067,563 12/1962 Dijk 2862 3,399,1088/1968 Olson 264-171 3,479,426 11/1969 Smedf 264-289 3,547,748 12/1970DOnofrio et al 264-346 3,561,082 2/1971 Stanley 264-346 3,618,30511/1971 Hilbert 2'8-62 FOREIGN PATENTS 10,763 4/1970 Japan 28--72.17

JAY H. WOO, Primary Examiner US. Cl. X.R.

28--71.3; 24218 R; 264210 F, 290 N, 345

